Upping the ante in the minutes before the Wednesday night explosion was what the plant contained - ammonium nitrate and anhydrous ammonia, both key ingredients in some fertilizers, which can be tricky when exposed to fire and the water used to fight it.

Ammonium nitrate is not considered explosive on its own under normal conditions, but a fire can turn it from solid fertilizer to a gas, and detonate.

Anhydrous ammonia - ammonia without water - must be stored under pressure in a liquid state, but in gas form it can ignite if exposed to water, such as a stream from a hose used in battling a blaze.

Whatever caused the explosion, it was huge; large enough to reportedly register 2.1 on the Richter scale used to measure earthquakes. By comparison, the explosion of the truck bomb packed with ammonium nitrate used to destroy the Alfred P. Murrah Federal Building in Oklahoma City in 1995 registered 3.0 on the scale.

The firefighters, several of whom are unaccounted for, would not have known if they had two minutes or a half-hour to decide.

Inspector Quvondo Johnson, of the Los Angeles County Fire Department, said if the West fertilizer plant contained both those chemicals, especially if near a civilian population, the concern would be for the possible explosion of the ammonium nitrate.

"That is what you would plan for," he said Thursday, stressing that he was not judging the actions of the Texas firefighters.

The tragedy has underscored the role of the state's 27,499 volunteer firefighters who despite often being underfunded and working for free, are the front lines of protection in most of rural Texas.

The West department, which dates to 1894, has 25 active volunteers, and has three fire engines, a water tender and a light rescue truck, according to the Texas A&M Forest Service.

Barron also said he would not judge the actions of those who were on the scene, saying only they know what they saw and heard at the time.

"There are a whole lot of unknowns," he said. "You never know what is on the other side of that door. You do your best to be prepared for anything."As they faced down the initial blaze, Barron said it was "very likely" that the volunteer firefighters did not have all the equipment they needed.

Volunteer fire departments get some of their funding from a state grant program that was sliced from $30 million to $7 million in the past two years, but is being restored, he said. They also turn to donations, cookouts and bake sales to raise money.

"The volunteer firefighters do the best they can with the limited resources they have," Barron said. "They have to make a dollar stretch very far. There is nothing cheap in fire service."